1. Field of the Invention
The present invention relates to a screw driving device and, more particularly, to a magnetic screw driving device that co-operates with a driving tool, such as a motorized tool, pneumatic tool or hand tool, for driving screws, screwdriver tips, drill bits or the like.
2. Description of the Related Art
A conventional driving device in accordance with the prior art shown in FIG. 8 comprises a driving shank 40 having a first end provided with a non-circular mounting post 43 and a second end formed with a non-circular mounting hole 41, and a magnetic member 42 secured in a bottom wall of the mounting hole 41 and extended into the mounting hole 41. When in use, the mounting post of the driving shank 40 is mounted on a driving tool, such as a motorized tool, pneumatic tool or hand tool, and the mounting hole 41 of the driving shank 40 is mounted on a driving member, such as a screwdriver tip, a drill bit and the like. At this time, the driving member is magnetically attracted by the magnetic member 42 so that the driving member is secured in the mounting hole 41 of the driving shank 40 exactly. Thus, the driving member is driven and operated by the driving tool. However, when the driving member is pushed backward due to an reaction, the driving member applies a pressure on the magnetic member 42 so that the magnetic member 42 is easily broken.
Another conventional driving device 50 in accordance with the prior art shown in FIGS. 9 and 10 comprises a socket 51 having a first end formed with a through hole 52, a second end formed with a non-circular mounting hole 53 and a mediate portion provided with a stop shoulder 54, a non-circular mounting post 56 secured in the through hole 52 of the socket 51, a magnetic member 55 movably mounted in the socket 51 and having a first end formed with a stop flange 551 received in the through hole 52 of the socket 51 and abutting the stop shoulder 54 of the socket 51 and a second end provided with a magnetic portion 554 extended into the mounting hole 53 of the socket 51, and an elastic member 553 received in the through hole 52 of the socket 51 and biased between the magnetic member 55 and the mounting post 56. The first end of the magnetic member 55 is formed with a receiving space 552 to receive the elastic member 553. Thus, when the driving member is pushed backward due to an reaction, the magnetic member 55 is pushed by the driving member to retract into the through hole 52 of the socket 51 and to compress the elastic member 553. Thus, the elastic member 553 provides a buffering effect to the magnetic member 55 to reduce the pressure applied on the magnetic member 55 so as to protect the magnetic member 55. However, it is difficult to form the stop shoulder 54 in the socket 51, thereby complicating the working process, and thereby increasing the cost of fabrication.
Another conventional driving device in accordance with the prior art shown in FIG. 11 comprises a driving shank 60, a magnetic member 63 movably mounted in the driving shank 60, a stop ring 66 secured in the driving shank 60 to stop the magnetic member 63, and an elastic member 64 mounted in the driving shank 60 and biased between the driving shank 60 and the magnetic member 63 to push the magnetic member 63 toward the stop ring 66. The driving shank 60 has a first end provided with a non-circular mounting post 66 and a second end formed with a non-circular mounting hole 61 and a receiving chamber 62 connected to the mounting hole 61. The receiving chamber 62 of the driving shank 60 has a peripheral wall formed with a retaining groove 65. The stop ring 66 is snapped into and secured in the retaining groove 65 of the driving shank 60 The magnetic member 63 is movably mounted in the receiving chamber 62 of the driving shank 60 and has a first end formed with a receiving space 68 to receive the elastic member 64 and a second end provided with a magnetic portion 69 extended into the mounting hole 61 of the driving shank 60. The magnetic member 63 has a peripheral wall formed with a stop flange 67 abutting the stop ring 66. Thus, the elastic member 64 provides a buffering effect to the magnetic member 63 to reduce the pressure applied on the magnetic member 63 so as to protect the magnetic member 63. However, it is difficult to form the retaining groove 65 in the receiving chamber 62 of the driving shank 60, thereby complicating the working process, and thereby increasing the cost of fabrication. In addition, the retaining groove 65 reduces the wall thickness of the receiving chamber 62 of the driving shank 60 to decrease the strength of the driving shank 60 so that the driving shank 60 is easily broken from the retaining groove 65.